Completely Automated Public Turing Test to Tell Computers and Humans Apart (CAPTCHA) based Robot Challenges for SIP

Document Type Expired Internet-Draft (individual)
Authors Hannes Tschofenig  , Eva Leppanen  , Saverio Niccolini  , Mayutan Arumaithurai 
Last updated 2008-02-25
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


A common approach to deal with unwanted communication attempts is to rely on some form of authorization policies, typically whitelists. In order to populate the entries in such an access control list it is helpful to have a way to challenge the entity willing to engage in a conversation (unless they are already pre-authorized). One reason why this is desired is to deal with robots that are aggressively distributing messages. This document describes how "Completely Automated Public Turing Test to Tell Computers and Humans Apart" (CAPTCHA) tests, which require human interaction, are applied to SIP.


Hannes Tschofenig (
Eva Leppanen (
Saverio Niccolini (
Mayutan Arumaithurai (

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)